The present invention relates to an organopolysiloxane fine particle, a process for producing the same and a liquid crystal display having the organopolysiloxane fine particles interposed as spacers between liquid crystal cell electrodes thereof. More particularly, the present invention is concerned with an organopolysiloxane fine particle which is excellent in spreadability and elastic properties, a process for producing the same and a liquid crystal display having the organopolysiloxane fine particles interposed as spacers between liquid crystal cell electrodes thereof.
It is common practice to interpose a spacer and seal a liquid crystal substance between a pair of electrodes disposed in a liquid crystal cell for liquid crystal display so that a liquid crystal layer is formed therebetween. When the thickness of this liquid crystal layer is not uniform, the image displayed on the liquid crystal cell may suffer from color shading (mottle) and contrast degradation at the time of lighting. Therefore, it is required that the thickness of the liquid crystal layer inside the liquid crystal cell be uniform. Further, when the displayed image is changed over at a high speed or when an image of a large visibility angle is displayed, it is also required that the thickness of the liquid crystal layer inside the liquid crystal cell be uniform.
Still further, for displaying large images free from color shading (mottle) on the currently employed large-scope liquid crystal display of STN mode, there is a greater need to have a uniform thickness of the liquid crystal layer inside the liquid crystal cell.
It is known to interpose, in dispersed form, spherical particles of uniform diameter between electrodes of the liquid crystal cell, namely to employ spherical particles as inter-electrode spacers of the liquid crystal cell, for making the thickness of the liquid crystal layer uniform inside the liquid crystal cell. For example, particles of an organic resin such as polystyrene and fine particles of silica are used as such spherical particles.
However, when particles of an organic resin such as polystyrene are used as the inter-electrode spacers of the liquid crystal cell, the problem is encountered such that the organic resin particles are so soft that it is difficult to maintain the uniformity of the thickness of the liquid crystal layer inside the liquid crystal cell. For example, if nonuniform pressure is applied to the liquid crystal layer inside the liquid crystal cell, the spacers are deformed in accordance with the nonuniformity of the pressure to thereby disenable maintaining the uniformity of the thickness of the liquid crystal layer inside the liquid crystal cell.
On the other hand, in case of fine particles of silica which are used as the inter-electrode spacers of the liquid crystal cell, when silica fine particles do not have a sharp particle diameter distribution, the problem that the thickness of the liquid crystal layer inside the liquid crystal cell is rendered nonuniform because of the smallness of the compressive deformation of the silica fine particles is invited. Furthermore, the problem is invited that, when such a liquid crystal display is exposed to low temperatures, void formation, namely cold (low-temperature) bubbling, occurs between the liquid crystal layer and the electrode of the liquid crystal cell because, inside the liquid crystal cell, the thermal expansion coefficient of the liquid crystal layer is different from that of the spacers.
In an attempt to solve the above problems, Japanese Patent Laid-open Publication No. 6(1994)-250193 proposed using as an inter-electrode spacer of liquid crystal cell silica fine particles prepared by first hydrolyzing a hydrolyzable silicon compound such as tetraethoxysilane to thereby obtain fine particles of silica and thereafter esterifying silanol groups present on silica particle surfaces with an organic compound.
The silica fine particle prepared by this process had appropriate hardness and mechanical recovery and was suitable to an inter-electrode spacer of liquid crystal cell. However, the mechanical recovery thereof was not highly satisfactory for use as an inter-electrode spacer of liquid crystal cell.
These fine particles having commonly been employed as spacer particles are composed of either an organic substance such as polystyrene or an inorganic substance such as silica and are substantially either hydrophobic or hydrophilic. Therefore, some of these fine particles, when to be spread in the wet state on an electrode base, are not monodispersed, depending on the type of solvent, to thereby disenable uniform spreading. Further, some of these fine particle, when to be spread in the dry state on an electrode base, are electrified to thereby disenable uniform spreading and invite such a problem that the fine particles are likely to stick to parts other than the electrode base.
As apparent from the above, even if a spacer fine particle has uniform particle diameters and excellent elastic properties, it may occur that uniform spreading thereof cannot be attained to thereby disenable satisfactory exertion of the effects based on their characteristics.
Japanese Patent Laid-open Publication No. 7(1995)-140472 discloses obtaining a spacer fine particle for liquid crystal cell having a specified compressive modulus of elasticity by subjecting an organosilicon compound of the formula Rxe2x80x2mSi(OR2)4-m (wherein each of Rxe2x80x2 and R2 represents a specified organic group, and m is an integer of 0 to 3) to hydrolysis, condensation polymerization and heating at 100 to 1000xc2x0 C. The compressive modulus of elasticity of the spacer fine particle is controlled by the amount of residual organic groups remaining after the pyrolysis of some of organic groups present in the interior of particles during the heating step.
However, there exists such a problem that, when particle diameters are different from each other, the amount of organic groups remaining in the particle interior after the heating step varies from particle to particle, so that control of the amount of residual organic groups is difficult to thereby increase the statistical dispersion of compressive modulus of elasticity from particle to particle with the result that it is difficult to control the compressive modulus of elasticity of the spacer fine particle for liquid crystal cell by the amount of residual organic groups remaining in the interior of particles. Furthermore, there exists such a problem that not only are the surface and the interior of particles different from each other in the amount of residual organic groups to thereby cause the compressive modulus of elasticity to be non-uniform throughout the whole body of particles, but also, voids occur at organic group portions in the internal part of particles thermally decomposed during the above heating step, with the result that the compressive modulus of elasticity of obtained spacer fine particle for liquid crystal cell is lowered.
Under these circumstances, the inventors found that producing an organopolysiloxane fine particle from an organosilicon compound by a specified process enables controlling the amount of organic groups in the interior of fine particles, even if the above heating step is not implemented, so that an organopolysiloxane fine particle of uniform particle diameter having a high elastic recovery can be obtained. Thus, the inventors made a proposal based on the finding (Japanese Patent Application No. 7(1995)-213800)(Japanese Patent Laid-Open Publication No. 9(1997)-59384).
However, the obtained organopolysiloxane fine particle was hydrophobic, so that it was experienced to be unable to effect uniform spreading thereof on a base, when the obtained organopolysiloxane fine particle was used as an inter-electrode spacer. Therefore, depending on the usage, it was needed to render part of the obtained hydrophobic organopolysiloxane fine particle hydrophilic. This necessitated additional treating steps for rendering the fine particle hydrophilic, etc., and, depending on the treatment, deterioration of the compressive strength of the organopolysiloxane fine particle was experienced.
The present invention has been made with a view toward solving the foregoing problems of the prior art. Therefore, it is an object of the present invention to provide fine particles for spacers which can be uniformly spread on an electrode base, having excellent elastic properties and having uniform particle diameters. It is another object of the present invention to provide a process for producing the spacer fine particle, and it is a further object of the present invention to provide a liquid crystal display having the spacer fine particle interposed as spacer between liquid crystal cell electrodes thereof.
The organopolysiloxane fine particle of the present invention comprises as a principal component a polysiloxane having a hydrocarbon group (a) directly bonded to a silicon atom and having an OH group (b) directly bonded to a silicon atom, wherein:
(i) carbons contained in the hydrocarbon group (a) constitute 5 to 35% of the weight of the organopolysiloxane fine particle, and
(ii) the OH group (b) is in an amount of 1 to 8 meq per g of the organopolysiloxane fine particle,
the organopolysiloxane fine particle having:
(iii) a 10% compressive modulus of elasticity of 150 to 900 Kg/mm2,
(iv) an average compressive deformation (Cr)m of 20 to 60%,
(v) an average elastic recovery (Rr)m of 60 to 90%, and
(vi) an average particle diameter of 0.5 to 50 xcexcm.
The statistical dispersion of the 10% compressive modulus of elasticity of the organopolysiloxane fine particle is preferably in the range of xc2x120% based on an average of the 10% compressive modulus of elasticity.
A process for producing an organopolysiloxane fine particle according to the present invention comprises the steps of:
(a) subjecting a mixture of an organosilicon compound of the formula Si(OR1)4 (1) and an organosilicon compound of the formula Rxe2x80x2Si(OR2)3 (2) to hydrolysis and condensation polymerization in a solvent of a mixture of water and an organic solvent to thereby obtain a dispersion of seed particles, provided that, in the formulae, each of R1 and R2 represents a hydrogen atom or an organic group having 1 to 10 carbon atoms selected from among an alkyl group, an alkoxyalkyl group and an acyl group, and Rxe2x80x2 represents an organic group having 1 to 10 carbon atoms selected from among substituted or unsubstituted hydrocarbon groups;
(b) adding an alkali to the dispersion of seed particles to thereby stabilize the seed particle dispersion;
(c), adding at least one compound represented by the following formula (3) or (4), optionally together with a compound represented by the following formula (5) while maintaining the seed particle dispersion at a pH of 6 to 9, to the seed particle dispersion and performing a hydrolysis and condensation polymerization thereof so that the seed particles are grown to thereby obtain a spherical fine particle dispersion, 
xe2x80x83wherein:
R2 and Rxe2x80x2 are as defined above, Rxe2x80x3 represents an organic group having 1 to 10 carbon atoms selected from among substituted or unsubstituted hydrocarbon groups, R3 represents a hydrogen atom or an organic group having 1 to 10 carbon atoms selected from among an alkyl group, an alkoxyalkyl group and an acyl group, and R4 represents a propyl or butyl group,
Y represents an organic group selected from among a methyl group, a methoxy group, an ethyl group and an ethoxy group, and M represents an element selected from among those of Groups 2 to 15 of the periodic table, and
m is an integer of 0 to 3 and n is an integer of 1 to 4, provided that m+n is an integer of 2 to 4;
(d) heating the spherical fine particle dispersion to thereby effect aging thereof; and
(e) treating the spherical fine particle in a moist atmosphere at 100 to 600xc2x0 C.
Another process for producing an organopolysiloxane fine particle according to the present invention comprise the steps of:
(a) subjecting a mixture of an organosilicon compound of the formula Si(OR1)4 (1) and an organosilicon compound of the formula Rxe2x80x2Si(OR2)3 (2) to hydrolysis and condensation polymerization in a solvent of a mixture of water and an organic solvent to thereby obtain a dispersion of seed particles, provided that, in the formulae, each of R1 and R2 represents a hydrogen atom or an organic group having 1 to 10 carbon atoms selected from among an alkyl group, an alkoxyalkyl group and an acyl group, and Rxe2x80x2 represents an organic group having 1 to 10 carbon atoms selected from among substituted or unsubstituted hydrocarbon groups;
(b) adding an alkali to the dispersion of seed particles to thereby stabilize the seed particle dispersion;
(c) adding at least one compound represented by the following formula (3) or (4), optionally together with a compound represented by the following formula (5) while maintaining the seed particle dispersion at a pH of 6 to 13, to the seed particle dispersion and performing a hydrolysis and condensation polymerization thereof so that the seed particles are grown to thereby obtain a spherical fine particle dispersion, 
xe2x80x83wherein:
R2 and Rxe2x80x2 are as defined above, Rxe2x80x3 represents an organic group having 1 to 10 carbon atoms selected from among substituted or unsubstituted hydrocarbon groups, R3 represents a hydrogen atom or an organic group having 1 to 10 carbon atoms selected from among an alkyl group, an alkoxyalkyl group and an acyl group, and R4 represents a propyl or butyl group,
Y represents an organic group selected from among a methyl group, a methoxy group, an ethyl group and an ethoxy group, and M represents an element selected from among those of Groups 2 to 15 of the periodic table, and
m is an integer of 0 to 3 and n is an integer of 1 to 4, provided that m+n is an integer of 2 to 4;
(d) heating the spherical fine particle dispersion to thereby effect aging thereof; and
(exe2x80x2) heating the spherical fine particle in a nitrogenous basic gas atmosphere.
The liquid crystal display of the present invention comprises a liquid crystal cell fitted with a pair of electrodes between which the above-mentioned organopolysiloxane fine particles are interposed as spacer.